Slowly reaction

Please, help my with my new Copter. I used APM2.8 on F450 frame.
I have one problem with slow reaction copter to left / right tilt (UP/DN reaction is OK). After the arming is this reaction more slowly.

What i´m doing bad ?

Here is link with my problem: https://youtu.be/QNP1lG2RmrU

Thanks you.

Petr.
PS: sorry for my english …